A last serves to substantially define the internal and external shape, as well as the overall geometry, of an article of footwear. Accordingly, the fit, function, and comfort of an article of footwear greatly depends upon the last from which it is derived. The last represents the footwear manufacturer's solution to the problem of finding a generic prescription for optimally accommodating the anatomical characteristics of a broad segment of the general public. The last is therefore an essential tool in the manufacture of an article of footwear and a well designed last is an extremely valuable commercial asset to a footwear manufacturer.
A last is the foot-shaped form or model over which an article of footwear is formed. A prior art last generally includes four main parts: the last block, a metal plate covering a portion or all of the sole area, a hinge in the middle of the last which allows the last to be divided for easy removal of the last from the shoe, and a thimble through the top and backpart of the last which allows a spindle to be inserted to hold the last during the shoemaking process.
Some of the common measurements which are taken into consideration when making a last are shown in FIGS. 1-4. As illustrated, the cone "c" for prior art last "L" is the upper portion extending from the ball portion to the top of the heel portion. The upper surface or top of the last is referred to as the cone island "ci". The last may also have an elevation of the toe tip that is measured from the tread point "tp" and a toe thickness "th" which defines the space given for the toes of the wearer of the footwear. The elevation of the toe tip is called toe spring "t". The ball or ball girth "b" of the last is the greatest dimension around the forefoot area of the last. The bottom of the last extends upwardly from the tread point "tp" to define the heel height "h". The short heel or short heel girth "sh" of the last is the dimension around a last passing through the instep and the heel feathering point. The instep or instep girth "i" is the dimension around the last passing through the instep point. Similarly, the waist or waist girth "w" is the smallest dimension around the last between the ball girth and the instep girth. As shown in FIG. 2, two common measurements for a last are the stick length "sl" and the bottom length "bl" which are taken by a measuring instrument called a stick. Further terms of art and measurements known to one of ordinary skill in the art are described in American Lastmaking, by Karl C. Adrian, published in 1991 by the Shoe Trades Publishing Company, of Arlington, Mass., the entire contents of which are hereby incorporated by reference.
Ideally, an article of footwear made on a last should guide the foot in a natural walking or running posture for optimum distribution of supportive and propulsive forces during each step. The article of footwear made on the last should also provide maximum comfort and freedom from excessive stress on the muscles, ligaments and tendons of the foot and leg. In prior art lasts, however, these objectives have not always been met. For example, the narrow cone shape present in many prior art lasts may produce an uncomfortable ankle region in the finished article of footwear. Further, the molding techniques and measurements utilized for making many lasts in the prior art generally do not take into consideration the curvature of the bottom of the foot, the first toe length and the weight which is borne by the finished article of footwear.